With the development of integrated circuit towards ultra-large scale integrated circuit, circuit density in the integrated circuit keeps increasing, the number of components included in the integrated circuit keeps increasing, and the size of the components decreases accordingly. With the decreasing of the size of semiconductor structures, channels of devices in the semiconductor structures are shortened accordingly. Because the channel is shortened, the gradient channel approximation of the devices is no longer valid, and varieties of adverse physical effects (especially a short-channel effect) become prominent. The device performance and reliability degrade, which limits further reduction of the size of the devices.
To control the short-channel effect, further reduction of device size requires further increase of a gate capacitance. The increase of the gate capacitance can be achieved by reducing a thickness of a gate dielectric layer. However, the decrease of the thickness of the gate dielectric layer will lead to the increase of a gate leakage current. To suppress the gate leakage current, a metal gate structure has been used in the semiconductor structure. The metal gate structure includes a metal electrode and a high-K dielectric layer. The metal gate structure can effectively increase the gate capacitance, and at the same time, effectively suppress the gate leakage current.
As the circuit density increases, a wafer surface cannot provide enough area to fabricate connection lines. To meet interconnection requirements of size-reduced components, a design of two and more layers of multi-layer metal interconnection lines has become one of common methods used in ultra-large scale integrated circuit technology. Plugs are used to connect the different metal layers or connect the metal layer and the semiconductor device.
With the reduction of the size of device, the reliability of the semiconductor structure still needs to be improved. The disclosed methods and device structures are directed to solve one or more problems set forth above and other problems.